Integrated proviruses of avian retroviruses are expressed by nuclear transcription into RNA which is processed, transported to the cytoplasm and translated. While the synthesis and processing of viral mRNAs are apparently accomplished by normal host enzymes, it is unclear whether the promoter(s) for synthesis intiation are located within the provirus or in neighboring host DNA. Our studies are designed to delineate the pathway of virus-specific RNA production with emphasis on the sites of RNA synthesis initiation. Employing cloned DNA segments and molecular hybridization, newly synthesized virus-specific RNAs will be identified and purified. The kinetics of appearance of potential precursors and intermediates as well as the mature RNAs, will be determined in pulse-chase studies. The purified RNAs, will be analyzed by nucleic acid hybridization, oligonucleotide "fingerprinting" and sequencing techniques to characterize and locate the sites at which synthesis is initiated and processing occurs.